Mixing apparatus



Aug. 21, 1956 F. M. ARCHIBALD I 2,759,711

MIXING APPARATUS Filed on. 1. 1952- 'FIGI-I DRIVING MECHANISM SHAFT 8 r 20 I I I I I I l l// MIXING VESSEL United States Patent NHXING APPARATUS Francis M. Archibald, Elizabeth, N. 1., assignor to Esso Research and Engineering Company, a corporation of Delaware Application October 1, 1952, Serial No. 312,535

3 Claims. (Cl. 259-24) The present invention concerns improvements in the art of mixing. More particularly, it relates to an 1mproved turbo-mixer especially suited for mixing heterogeneous liquid phases. The improvement in a turbomixer comprises a hollow spindle that is concentric with and forms an annular liquid passageway with the 1mpeller shaft of the turbo-mixer. The hollow spindle is free to rotate independently of the impeller shaft and preferably in an opposite direction. Further, the spindle is provided with means for introducing a liquid within the annular passageway and also means for convey ng the liquid within the annular passageway to a position within the throat of the turbo-mixer impeller. The present invention has particular application in the petroleum industry in the form of an improved method and apparatus for chemically treating hydrocarbon oils. In this connection, the present invention is especially concerned with the sulfuric acid treatment of highly refined white oils.

Turbo-mixers, or turbine mixers as they are also known, have found wide application in industry for a variety of mixing problems. Their high mixing efiiciency and relatively low power consumption make them very attractive.

The simplest type of turbo-mixer consists of an impeller mounted on a drive shaft which is rotated within a body of liquid. The impeller itself consists of a plurality of blades attached circumferentially about the im peller shaft with ports that permit liquid to enter within the impeller at a point near the hub, and thence to flow out along the blades. The blades may be straight, in that they extend radially from the center of the shaft, or they may be curved either forward or backward relative to the direction of rotation of the shaft. In addition, the blades may be either open or shrouded so as to better direct the flow of liquid through the impeller.

As the impeller revolves within a body of liquid the liquid flows axially along the impeller shaft until it enters the throat or eye of the impeller proper. At this point the liquid is diverted vertically away from the impeller shaft and flows out through the revolving impeller blades. The blades act to thoroughly mix the liquids passing through them and also to insure uniform mixing of the entire body of liquid. The action of a turbo-mixer is not unlike the action of a centrifugal-type pump which takes a suction along its impeller hub and then discharges the liquid from the tips of its impeller blades.

A conventional turbo-mixer may be from 6 inches to 3 feet in diameter; it may have speeds of 200 to 3000 R. P. M.; and there may be one or more impellers positioned on the same impeller shaft. In addition, an impeller may take suction on one or both sides of the impeller and it may be constructed out of a wide variety of materials, depending largely upon the application to which it is to be put.

Many turbo-mixers are also provided with a stationary ring of blades, called a stator, that surrounds and is in close proximity to the rotating impeller. These stationary blades may be straight, or curved in either a 2,759,7i1 Patented Aug. 21, 1956 backward or forward manner similar to the blades of the impeller. In general, the action of the stator is to catch the liquid as it is spun from the impeller and to redirect it radially from the impeller shaft. The clearance between the stator and the impeller is generally very small, thus imposing a shearing force on the liquid that assists greatly in the mixing operation.

Turbo-mixers are conventionally employed within suitable mixing tanks or vessels. The materials to be mixed are usually charged to the vessel through suitable openings such as valves, and the mixed products are generally withdrawn from the vessel through a valve located at the vessels bottom. Generally speaking, the vessels themselves are cylindrical in shape and have dished or rounded bottoms in order to promote good mixing.

In some instances, it is preferred to add one or both of the materials to be mixed to the vessel in small increments. This is often true in the petroleum industry, where a chemical such as sulfuric acid is used to treat a hydrocarbon oil. In this case the hydrocarbon oil is charged to a mixing vessel and the sulfuric acid then added gradually to the oil while the latter is being actively mixed. At the present time, sulfuric acid is merely added through a suitable valve in the top of the vessel and drops or otherwise enters into the main body of the oil. The mixing device then gradually mixes and disperses the sulfuric acid throughout the entire body of oil.

It is apparent that conventional mixing techniques have several disadvantages in handling mixing problems such as the one just described-namely, the mixing of sulfuric acid and hydrocarbon oil. In this particular case, for example, incomplete or non-instantaneous dispersion of the fresh sulfuric acid within the oil permits the fresh acid to come into contact and interreact with the reaction end products formed by previously dispersed acid. The result is that the fresh acid is used inefliciently, and that undesirable amounts of degradation products are formed.

It will also be noted in the sulfuric acid treating of a hydrocarbon oil that a large amount of heat is generated when these two liquids react with each other. For this reason the mixing vessels employed in this and similar processes are provided with cooling coils to remove the heat as it is released. The success of such coils depends, of course, upon the heat of reaction being released before or at the time of the fluid flow through the coils. If the release of heat is delayed by poor mixing, the coils may be largely ineffectual in fulfilling their purposethat of preventing excessive temperatures. These and other shortcomings associated with non-instantaneous forms of mixing equipment, while undesirable in batch mixers, are particularly so in continuous mixers.

Accordingly, it is an object of the present invention to provide means for greatly decreasing the time required in a mixing vessel for intermixing various materials. It is a particular object of the present invention to provide mixing apparatus in which two heterogeneous liquid phases are mixed substantially instantaneously upon contact. It is a particular object to provide a turbo-mixer in which one liquid is added to a second liquid at a point within the throat of the turbo-impeller, whereby the two liquids are more efiiciently and rapidly mixed than has been heretofore possible. In this connection, it is an additional object to impose a shearing force on two heterogeneous liquid phases immediately as they contact one another for the purpose of insuring more complete and instantaneous intermixing of the phases.

The present invention, as applied to conventional turbomixers, consists in providing a turbo-mixer with a hollow spindle which is concentric with and forms an annular space with the impeller shaft of the mixer. Each end of the hollow spindle is preferably movably sealed either directly or indirectly to the impeller shaft and is thereby free to rotate independently of the shaft. Conventional means are provided for introducing a liquid within the annular space between the spindle and the shaft; and means are also provided for permitting liquid within the annular space to enter the throat of the impeller. This latter means is preferably in the form of an orifice or a plurality of fluid passageways adapted to jet the liquid into the throat of the impeller. This type of action is desired for the reason that a shearing force is exerted upon the liquid flowing from the annular space into the throat of the impeller by the liquid or liquids Plr present in the impeller throat. In this connection, it IS preferred that the spindle rotate at a different speed than the impeller shaft and preferably in an opposite direction.

The present invention may be better understood by reference to the attached figures which illustrate a pre ferred embodiment of the invention.

Fig. 1 depicts a preferred form of a turbo-mixing apparatus of the type defined herein.

Fig. 2 is a transverse section taken through plane lIII of the apparatus illustrated in Fig. 1.

Referring first to Fig. 1, it will be noted that the apparatus shown includes a number of conventional items such as a mixing vessel 3, inlet and outlet connections 27 and 30, an impeller 14, an impeller shaft 8, a driving mechanism 7, and a stator ring 13. Novel features of the apparatus include hollow distributing spindle it), which is provided with a small fluid passageway or orifice 28. Passageway 28 is positioned such that liquid contained within annular space 26 can flow directly into the throat 29 of impeller 14. Spindle It) is movably sealed as by rotary seals and 16. Seal 15 is positioned between the impeller end of shaft 8 and the corresponding end of spindle it while seal 16 is positioned between the opposite end of spindle It and a stationary adapter 13. The seals 15, 16 and 17 are represented in Fig. 1 as labyrinth type seals, but any form of seal which will permit relative rotation of shaft 8 and the spindle it may be employed. Adapter 18 is further provided with a rotary seal 17, positioned between the adapter and shaft 8. It will be noted that distributing spindle It may be of a length such that adapter 18 may be positioned within vessel 3, but it is preferred that adapter 18 be placed outside vessel 3, as illustrated. Adapter 18 is further provided with a conduit 25 for permitting the introduction of a liquid within annular space as.

In Fig. l, impeller 14 and shaft 8 are driven directly by driving mechanism 7, which may be of any conventional hydraulic, pneumatic, or electrical type. Spindle 10 is driven by means of a gear train consisting of gears 22, 21, and 29. Gear 21, attached to shaft 23, is sup ported as by means of member 24, which may be a pillow block or other type of bearing support. It is apparent from the relationship of gears 20, 21, and 22 that gear 22 rotates in a direction opposite to that of gear 20. The speed of spindle 10 relative to the speed of shaft 3 in this instance is obviously determined by the relative diameters of gears 20, 21, 21a and 22 and the number of teeth thereon. It is preferred that spindle I and shaft 8 rotate in opposite directions, and that spindle It) have a speed of about 2 /2 to 5 times that of shaft 8. In the drawing, the gears, as shown, represent a relationship adapted to obtain the desired result with a ratio of 2 /2 to 1 between the gears and 21 and a 1 to 1 ratio between gears 21a and 22. Conversely, shaft 8 may have a speed of about 2 /2 to 5 times that of spindle 10. The absolute speed of shaft 8 will, of course, vary with the viscosity of the liquid, the power required, the sizes of the impeller and the vessel. For example, in sulfuric-acid treating a 400 gallon charge of oil, in a vessel equipped with a 24" diameter agitator, it is desirable to use shaft speeds of about 350 to 400 R. P. M.

Vessel 3 may be either open or closed. In Fig. l, vessel 3 is depicted as being a closed vessel having a solid top 6, which is pierced by conduit 27 and spindle 10. A rotary seal, represented as a labyrinth type seal 9 prevents liquid or vapors from escaping along spindle 10.

When mixing two heterogeneous liquid phases such as a hydrocarbon oil and sulfuric acid, the apparatus shown in Figs. 1 and 2 may be operated in the following manner. A hydrocarbon oil such as a lubricating oil, heating oil, gasoline, etc. is charged to vessel 3 through line 27 and valve 4. Driving mechanism 7 is started and drives shaft 8 and attached impeller 14 in one direction and drives spindle it) in the opposite direction. The motion of the impeller causes oil to be drawn through throat 29 and thrown out by blades 12 of the impeller through the blades 31 of the stator. Support for the stator may be provided in any suitable manner, as by uprights indicated by the numeral 32.

Sulfuric acid of to oleum strength is pumped or otherwise introduced through line 25 and stationary adapter 18 into annular space 26 from which it flows through opening 28 into throat 29 of the impeller. Conventional operating conditions such as the amounts of oil and acid charged, the treating temperature, treating time, etc. may be employed. The impingement of the acid from opening 23 on the liquid flowing through throat 29 as caused by the relative motion of spindle It) and impeller 14 is such that shearing forces are set up which disperse the acid throughout the oil. The position and movement of orifice or opening 23 is uniquely advantageous, in that the acid and oil are intimately contacted with each other at a time and point just prior to their mutual passage through blades E2 of impeller 14 and blades 31 of stator 12'. Thus the acid and oil are thoroughly and efiiciently mixed in the proper concentration as soon as they contact each other within vessel 3, with the desirable result that the acid is substantially instantaneously dispersed throughout the oil. Thus, the treating ability of the acid is utilized to a very high degree.

After all of the necessary acid has been added, and after the required treating time has been employed, driving mechanism 7 is stopped and the liquid mixture in vessel 3 allowed to separate into an upper hydrocarbon layer and an acid layer. The acid layer is withdrawn through line 30 and valve 5 to any conventional processing step or apparatus. The hydrocarbon layer may then also be drawn off through line 30 in the same manner, or it may be neutralized with caustic or other treating agent directly within vessel 3, and then removed through line 30. These latter steps are conventional in the art and it is not felt necessary to describe them in detail here. The operating parts of the turbo-mixer, including the impeller, stator, shaft 8 and spindle 10 may be made from any conventional materials, such as carbon steel, stainless steel, Monel, brass, glass, or ceramic-coated metals, cast iron, etc. Seals 15, 16, 17, and 9 may be packing glands, or any one of a number of conventional rotary joints or mechanical seals. In addition, the apparatus described may be employed in a wide variety of mixing applications and particularly where heterogeneous liquid phases are involved.

What is claimed is:

1. In a turbo-mixer including an impeller, a stator, an impeller shaft, and a driving mechanism, wherein said impeller has a throat portion opening therefrom adjacent said shaft the improvement which comprises a hollow spindle concentrically disposed and forming an annular space about said shaft, one end of said spindle terminating and being movably sealed to the impeller end of said shaft, within said impeller throat the opposite end being movably sealed to a stationary hollow adapter, said adapter in turn being movably sealed to said shaft, means for introducing a liquid within said annular space, at least one liquid passageway defined in said spindle and arranged to jet liquid from said annular space into the throat of said impeller, and means for rotating said spindle at a speed of about 2 /2 to 5 times that of said impeller.

2. In a turbo-mixer including an impeller, a stator,

an impeller shaft and a driving mechanism, wherein said impeller has a throat portion opening therefrom adjacent said shaft the improvement which comprises a hollow spindle movably sealed to and forming an annular space with said shaft, one end of said spindle extending into and terminating within said impeller throat means for introducing a liquid within said annular space, at least one liquid passageway defined in said spindle and arranged to jet said liquid into the throat of said impeller and means for driving said spindle and said impeller rotationally at difierent speeds relative to one another.

3. Apparatus as defined in claim 2, wherein the spindle and the impeller rotate in opposite directions.

References Cited in the file of this patent UNITED STATES PATENTS Fay Jan. 2, 1917 Lambie Jan. 15, 1918 Maitland Apr. 3, 1923 Rogler Dec. 30, 1924 Wheelwright July 15, 1941 Huif Apr. 25, 1944 Hervert June 12, 1945 Tatman Oct. 21, 1952 

1. IN A TURBO-MIXER INCLUDING AN IMPELLER, A STATOR, AN IMPELLER SHAFT, AND A DRIVING MECHANISM, WHEREIN SAID IMPELLER HAS A THROAT PORTION OPENING THEREFROM ADJACENT SAID SHAFT THE IMPROVEMENT WHICH COMPRISES A HOLLOW SPINDLE CONCENTRICALLY DISPOSED AND FORMING AN ANNULAR SPACE ABOUT SAID SHAFT, ONE END OF SAID SPINDLE TERMINATING AND BEING MOVABLY SEALED TO THE IMPELLER END OF SAID SHAFT, WITHIN SAID IMPELLER THROAT THE OPPOSITE END BEING MOVABLY SEALED TO A STATIONARY HOLLOW ADAPTER, SAID ADAPTER IN TURN BEING MOVABLY SEALED TO SAID SHAFT, MEANS FOR INTRODUCING A LIQUID WITHIN SAID ANNULAR SPACE, AT LEAST ONE LIQUID PASSAGEWAY DEFINED IN SAID SPINDLE AND 